/*
 * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
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 * modification, are permitted provided that the following conditions
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 *
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 *   - Redistributions in binary form must reproduce the above copyright
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 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle or the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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package me.joshua.arsenal4j.java.demo.spi;

import java.util.Iterator;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;

public class DictionaryService {

	private static DictionaryService service;
	private ThreadLocal<ServiceLoader<Dictionary>> localLoader;

	private DictionaryService() {
		// ServiceLoader实例线程不安全
		localLoader = new ThreadLocal<ServiceLoader<Dictionary>>() {
			@Override
			protected ServiceLoader<Dictionary> initialValue() {
				// 加载服务
				return ServiceLoader.load(Dictionary.class);
			}
		};
	}

	public static synchronized DictionaryService getInstance() {
		// 单例，便于获取使用
		if (service == null) {
			service = new DictionaryService();
		}
		return service;
	}

	public String getDefinition(String word) {
		String definition = null;

		try {
			// 遍历并调用服务
			Iterator<Dictionary> dictionaries = localLoader.get().iterator();
			while (definition == null && dictionaries.hasNext()) {
				Dictionary d = dictionaries.next();
				definition = d.getDefinition(word);
			}
		} catch (ServiceConfigurationError serviceError) {
			definition = null;
			serviceError.printStackTrace();

		}
		return definition;
	}
}
